Electrochromic devices reflect, absorb or transmit a controllable amount of light in response to an input of electric current to the device. Electrochromic devices have a wide range of applications, e.g., a variably tintable window for an automobile or building. Many electrochromic devices include an electrochromic electrode, an ion conductor and a counterelectrode.
Iridium oxide can be used in the electrochromic electrode or the counterelectrode of an electrochromic device as disclosed in U.S. Pat. No. 4,258,984 to Beni et al.
A preferred electrochromic device of U.S. Pat. No. 5,124,080 to Shabrang and Babinec comprised a layered structure as follows: (1) a panel of glass; (2) a layer of indium tin oxide upon the panel of glass; (3) a layer of tungsten oxide upon the layer of indium tin oxide; (4) a layer of perfluorosulfonic acid polymer upon the layer of tungsten oxide; and (5) a layer of gold upon the layer of perfluorosulfonic acid polymer. The layer of tungsten oxide and the layer of indium tin oxide form the electrochromic electrode. The layer of perfluorosulfonic acid polymer is the ion conductor. The layer of gold is the counterelectrode.
The above described electrochromic devices performed well, especially when operated in a humidified inert gas environment as disclosed in U.S. Pat. No. 5,136,419 to Shabrang. For example, such electrochromic devices have operated for tens of thousands of cycles. However, when the size of such devices was increased from square inch dimensions to square foot dimensions, then an unforeseen problem arose with the gold layer. The problem was the apparent failure of the gold layer after less than one thousand cycles.